Reversed dye-sensitized photovoltaic cell

ABSTRACT

The invention provides a solar cell or photovoltaic element  1,  which is a layered structure or stack  25,  comprising a flexible conductive composite foil  23,  including a support material layer foil  23   b  and a first electrically conductive layer  23   a,  an oxide layer  28,  a crystalline metal-oxide semi-conductor  26  layer  14,  a photosensitization material  15,  an electrolytic liquid (or other  18  hole conducting medium)  16,  a catalyst layer  19,  a transparent second electrically conductive layer  18  and transparent flexible substrate  26.

FIELD OF THE INVENTION

The invention relates to a photovoltaic element comprising a layeredstructure of at least a first electrically conductive layer, a layer ofcrystalline metal oxide semiconductor material deposited on the firstelectrically conductive layer, a transparent second electricallyconductive layer deposited on a transparent substrate and an holeconducting medium contained between the layer of semiconductor materialand the second electrically conductive layer.

BACKGROUND OF THE INVENTION

Such an element is known from the U.S. Pat. No. 4,927,721. This patentdiscloses a photo-electrochemical cell comprising a polycrystallinemetal oxide semiconductor layer having a substantially monomolecularchromophore layer in a surface zone. The metal oxide semiconductor layeris a TiO₂-layer having a roughness factor of preferably more than 200,deposited on a Ti-substrate. The TiO₂-layer is obtained by a processwhich is repeated several times, according to which a titanium-ethoxidesolution in methanol is applied to the titanium substrate, after whichthe resulting titanium alkoxide is hydrolyzed and heated.

Known from the U.S. Pat. No. 5,350,644 is a photovoltaic cell, whichcomprises a light-transmitting electrically conductive layer which isdeposited on a glass plate or a transparent polymer foil to which anumber of preferably porous layers of titanium dioxide have been appliedand wherein at least the last titanium dioxide layer is doped with adivalent or trivalent metal ion. The combination of titanium dioxide andconductive layer forms the photo electrode of a solar cell, which solarcell further comprises a light-transmitting second electricallyconductive layer which is deposited on a light-transmitting substrateand which forms a counter-electrode. Received between photo electrodeand counter-electrode is an electrolyte acting as redox system.

The operation of known solar cells, such as for instance described inU.S. Pat. No. 4,927,721, is as follows. A photon from the visible lightincident via the photo-electrode or counter-electrode releases anelectron at the interface of titanium dioxide and electrolyte from anelectron-hole combination, which electron disappears in the conductionband of the titanium dioxide and is discharged via the electricallyconductive layer of the photo electrode. The resulting hole issupplemented with an electron from the electrolyte, while theelectrolyte accepts an electron from the counter electrode. Theacceptance of electrons by the electrolyte can be enhanced by a catalystapplied to the surface of the counter-electrode, while the efficiency ofthe solar cell can be increased by a sensitizer dye on the surface ofthe titanium dioxide layer, which dye absorbs light and herein acquiresan energy-rich state and is able to inject an electron with anefficiency of almost 100% into the conduction band of the titaniumdioxide.

WO 99/66520 describes a photovoltaic element comprising a layeredstructure of at least a first electrically conductive layer, a layer ofcrystalline metal oxide semiconductor material deposited on the firstelectrically conductive layer, a transparent second electricallyconductive layer deposited on a transparent substrate and anelectrolytic liquid contained between the layer of semiconductormaterial and the second electrically conductive layer, wherein the layerof semiconductor material is deposited on a metal foil, which metal foilforms the first electrically conductive layer.

Yongseok Jun et al. describes in Solar Energy Materials & Solar Cells 91(2007) 779-784, a steel-based dye-sensitized solar cell.

Seigo Ito et al. describes in Chem. Commun. 2006 4004-4006 ahigh-efficiency flexible dye-sensitized solar cell with Ti-metalsubstrate for nanocrystalline TiO₂ photo anode.

W. A. Gazotti et al describes in Synthetic metals 108 (2000) 151-157 aflexible photo electrochemical device based on conducting polymers.

U.S.2006/0062902 describes CIGS (Cu, In, Ga, Se/S) absorber layersfabricated using coated semiconducting nanoparticles and/or quantumdots. Core nanoparticles and/or quantum dots containing one or moreelements from group IB and/or IIIA and/or VIA may be coated with one ormore layers containing elements group IB, IIIA or VIA. Usingnanoparticles with a defined surface area, a layer thickness could betuned to give the proper stoichiometric ratio, and/or crystal phase,and/or size, and/or shape. The coated nanoparticles could then be placedin a dispersant for use as an ink, paste, or paint. By appropriatecoating of the core nanoparticles, the resulting coated nanoparticlescan have the desired elements intermixed within the size scale of thenanoparticle, while the phase can be controlled by tuning thestochiometry, and the stoichiometry of the coated nanoparticle may betuned by controlling the thickness of the coating(s).

SUMMARY OF THE INVENTION

Such a known solar cell has a number of disadvantageous properties whichstand in the way of large-scale application of this cell. Inherent inthe use of glass as transparent substrate material is a determinedthickness and stiffness of a solar cell which makes the cell unsuitablefor use, for instance in particular products in the field of consumerelectronics, such as watches. It is known that replacing glass with atransparent flexible plastic may result in a loss of efficiency of thesolar cell.

It is especially an object of the invention to provide a solar cell ofvery small thickness which has a high efficiency when transparentpolymer foil is used and which can be assembled in large quantities in asimple manner.

It is further an objective to provide an alternative solar cell (hereinalso indicated as “photovoltaic cell” or “PV” cell or “photovoltaicelement”), which preferably does not suffer from above-mentioneddisadvantages and/or preferably provides the above described desiredproperties.

This objective may be achieved and other advantages may be gained with aphotovoltaic element, such as of the type stated in the preamble,wherein according to the invention the layer of semiconductor materialis deposited on a flexible conductive composite foil, which flexibleconductive composite foil provides the first electrically conductivelayer.

In the solar cell according to the invention light impinges upon thesemiconductor material via the transparent counter-electrode and theelectrolytic liquid (or other hole conducting medium) between thecounter-electrode and the semiconductor material.

The most obvious manner of light incidence in the known cell, i.e. viathe photo electrode, is precluded by use of the non-transparent flexibleconductive composite foil. A photovoltaic element according to theinvention is a “reversed solar cell”.

Surprisingly, it has now been found that the efficiency of a reversedsolar cell according to the invention may be higher than in a known,above described solar cell (with both electrodes comprising plasticmaterial), wherein the photo electrode is impinged upon directly, andnot via the electrolytic liquid (or other hole conducting medium), bythe photons of incident sunlight. A cause of the recorded increase inefficiency is sought in the fact that application of a flexibleconductive composite foil as substrate material enables sintering of thelayer of semiconductor material at higher temperatures than in a knownsolar cell with a substrate of polymer material.

Further, the flexible conductive composite foil may be relatively easyto make, and/or simple to process and/or may have relatively highmechanical strength, relative to other foils, such as a pure titanium(Ti), tin (Sn) or zinc (Zn) foil. A further advantage may be that theelectrically conductive layer is substantially protected from theenvironment by the support material layer foil. Yet another advantage isthat as support material layer foil material abundantly availablematerials (such as in the form of commercially available foils) may beapplied.

Therefore, the invention especially provides a photovoltaic element (orsolar cell), comprising a layered structure, wherein the layeredstructure comprises:

-   -   a. flexible conductive composite foil including a support        material layer foil and a first electrically conductive layer        (preferably a layer selected from the group consisting of a        titanium layer, a tin layer and a zinc layer); the first        electrically conductive layer in contact with    -   b. an oxide layer; the oxide layer in contact with    -   c. a crystalline metal-oxide semi-conductor layer; the        crystalline metal-oxide semi-conductor layer in contact with    -   d. a photosensitization material; the photosensitization        material in contact with    -   e. a hole conducting medium; the hole conducting medium in        contact with    -   f. a catalyst layer; the catalyst layer in contact with    -   g. a transparent second electrically conductive layer; and the        transparent second electrically conductive layer in contact with    -   h. a transparent substrate (especially a flexible transparent        substrate).

Such layered structure or stack as solar cell may be flexible, efficientand stable.

In a preferred embodiment, the flexible conductive composite foil maycomprise a laminate comprising a support material layer foil and thefirst electrically conductive layer. Herein, a support material layer inthe form of a foil is indicated as “support material layer foil”.

In general, the support material layer foil may be selected from thegroup consisting of iron foil, iron alloy foils, steel foils (includingfor instance foils of carbon steel, stainless steel, HSLA steel (highstrength low alloy), or tool steel), aluminium foil, copper alloy foils,brass (CuZn) foils, resistance foils (CuNi), nickel foils, silver foils,nickel silver foils, iron nickel foils (such as invar), and the firstelectrically conductive layer may comprise a layer selected from thegroup consisting of a titanium layer, a tin layer and a zinc layer.

In an embodiment, the support material layer foil comprises an iron foilor an iron alloy foil and the first electrically conductive layercomprises a titanium layer. In another embodiment, the support materiallayer foil comprises an iron foil or an iron alloy foil, and the firstelectrically conductive layer comprises a tin layer. In anotherembodiment, the support material layer foil comprises an iron foil or aniron alloy foil, and the first electrically conductive layer comprises azinc layer. Especially, the foil comprises an iron alloy foil, such as asteel foil. In another embodiment, the support material layer foilcomprises an aluminium foil and the first electrically conductive layercomprises a titanium layer. In another embodiment, the support materiallayer foil comprises an aluminium foil and the first electricallyconductive layer comprises a zinc layer. In yet another embodiment, thesupport material layer foil comprises an aluminium foil and the firstelectrically conductive layer comprises a tin layer.

Such laminate comprising a support material layer foil and the firstelectrically conductive layer may for instance be obtained by providinga support material layer foil and depositing thereon the firstelectrically conductive layer. Deposition may in an embodiment beelectrochemical deposition, may be spray pyrolysis or chemical vapourdeposition (optionally followed by calcination to provide the oxideskin). In another embodiment, deposition may comprise sputtering. Othertechniques known in the art may also be applied. An advantage of thelaminate comprising a support material layer foil and the firstelectrically conductive layer is that the first electrically conductivelayer may be very thin, such as in the range of about one atomic layer(about 0.1 nm) up to about 100 nm. However, the layer thickness of thefirst electrically conductive layer may also be up to about a 1 μm.Especially, the first electrically conductive layer and the oxide layertogether have a layer thickness in the range of about 20-100 nm.However, the layer thickness of the first electrically conductive layerand the oxide layer together may also be up to about 2 μm.

In a specific embodiment, the laminate comprising a support materiallayer foil and the first electrically conductive layer is obtainable byproviding a first metal doped second metal layer foil, wherein the firstmetal comprises one or more metals selected from the group consisting oftitanium, zinc and tin, and wherein the second metal layer foilcomprises a metal layer foil, especially selected from the groupconsisting of iron foil, iron alloy foils, steel foils (including forinstance foils of carbon steel, stainless steel, HSLA steel (highstrength low alloy), or tool steel), aluminium foil, copper alloy foils,brass (CuZn) foils, resistance foils (CuNi), nickel foils, silver foils,nickel silver foils, iron nickel foils (such as invar), and providing aheat treatment to the first metal doped second metal layer foil. Becauseof the heat treatment, the first metal may migrate to the surface of thesecond metal layer foil, and may form the first electrically conductivelayer on the second metal layer foil, thereby providing in an embodimentthe laminate comprising a support material layer foil and the firstelectrically conductive layer.

In yet another embodiment, the laminate comprising a support materiallayer foil and the first electrically conductive layer comprises alaminate of a conductive polymer and the first electrically conductivelayer.

In a further embodiment, the flexible conductive composite foilcomprises a laminate of a support material layer foil and anelectrically conductive layer foil (as first electrically conductivelayer). For instance, the laminate may comprise a laminate of an ironfoil or an iron alloy foil, and a titanium foil. Such foils may beobtained by laminating (like rolling) the foils to each other. Again,the support material layer foil may be selected from the groupconsisting of iron foil, iron alloy foils, steel foils (including forinstance foils of carbon steel, stainless steel, HSLA steel (highstrength low alloy), or tool steel), aluminium foil, copper alloy foils,brass (CuZn) foils, resistance foils (CuNi), nickel foils, silver foils,nickel silver foils, iron nickel foils (such as invar), and theelectrically conductive layer foil (as first electrically conductivelayer) may comprise a foil selected from the group consisting of atitanium foil, a tin foil and a zinc foil.

In this embodiment, the layer thickness of the first electricallyconductive layer foil may for instance be in the range of about 5-200μm, especially 10-100 μm. Hence, the layer thickness of the firstelectrically conductive layer foil and the oxide layer together may alsobe in the range of about 5-200 μm, especially 10-100 μm.

Referring to the support material layer foil as described above in anumber of embodiments, especially preferred support material layer foilsare those comprising iron or iron alloys, such as steel foils (includingfor instance foils of carbon steel, stainless steel, HSLA steel (highstrength low alloy), or tool steel), and iron nickel foils (such asinvar). The support material layer foil is in contact with the firstelectrically conductive layer.

With the use of zinc, tin or titanium a skin of zinc oxide, tin oxide,respectively titanium oxide may result when the semiconductor layerdeposited thereon is sintered, which “skin” on the one hand may providea protection for the underlying zinc, tin, respectively titanium, and onthe other hand may provide a good electrical conductor owing to itsphotoelectric properties. Oxide skins of the metal of the firstelectrically conductive layer are herein also indicated as “nativeoxides” or “native oxide skins”.

Alternatively (or optionally also additionally), a non-native oxide(“skin”) may be provided. For instance, a zinc oxide layer may beprovided to a first electrically conductive layer comprising titanium,or a titanium oxide layer may be provided to a first electricallyconductive layer comprising zinc, etc. Such non-native oxide layer mayfor instance be provided by providing a multi-layer comprising atitanium layer (attached to the support material layer foil) and a zinclayer (oxide precursor layer) or alternatively a zinc layer (attached tothe support material layer foil) and a titanium layer (oxide precursorlayer), wherein (at least part of) the latter layers (i.e. the zinc andtitanium oxide precursor layer, respectively) are oxidized to form anoxide, during sintering the semiconductor layer to this oxide precursorlayer. Such non-native oxide may for instance be provided by deposition,which may in embodiments be electrochemical deposition, may be spraypyrolysis or chemical vapour deposition (optionally followed bycalcination to provide the oxide skin).

Hence, the oxide layer may be selected from the group consisting of anative-oxide layer or a non-native oxide layer, and may comprise one ormore oxides selected from the group consisting of titanium oxide, tinoxide and zinc oxide.

Herein, instead of zinc or titanium, also a titanium zinc alloy may beapplied; i.e., the first electrically conductive layer and/or the oxidelayer may comprise an alloy or mixed oxide, respectively. Hence, thenative oxide or the non-native oxide layer may also be a mixed oxide(i.e. mixed titanium oxide zinc oxide).

Therefore, the first electrically conductive layer may comprise one ormore metals selected from the group consisting of titanium, zinc andtin. Hence, the phrase “a layer selected from the group consisting of atitanium layer, a tin layer and a zinc layer” in an embodiment alsorefers to a layer comprising one or more metals selected from the groupconsisting of titanium, zinc and tin. Titanium or titanium alloys, andespecially titanium, are preferred as first electrically conductivelayer.

Likewise, the oxide layer may comprise one or more oxides selected fromthe group consisting of titanium, zinc and tin. The oxide layer maycomprise one or more native metal oxides, as a result of oxidation ofthe top layer of the first electrically conductive layer (i.e. nativeoxides or native oxide layer).

In a further aspect, the invention provides a photovoltaic element,wherein the oxide layer is the first electrically conductive layer.Therefore, the invention especially provides a photovoltaic element (orsolar cell), comprising a layered structure, wherein the layeredstructure comprises:

-   -   a. flexible conductive composite foil, including        -   i. a support material layer foil and        -   ii. a first electrically conductive layer, wherein the first            electrically conductive layer is a conductive oxide layer;            the first electrically conductive layer in contact with    -   b. a crystalline metal-oxide semi-conductor layer; the        crystalline metal-oxide semi-conductor layer in contact with    -   c. a photosensitization material; the photosensitization        material in contact with    -   d. a hole conducting medium; the hole conducting medium in        contact with    -   e. a catalyst layer; the catalyst layer in contact with    -   f. a transparent second electrically conductive layer; and the        transparent second electrically conductive layer in contact with    -   g. a transparent substrate (especially a flexible transparent        substrate).

Preferably, the first electrically conductive layer is a layer obtainedby providing a metallic layer and oxidizing said metallic layer toprovide the conductive oxide layer. The layer may be oxidized entirelyor partly. In a specific embodiment, the metallic layer is selected fromthe group consisting of a titanium layer, a tin layer and a zinc layer.In this way, the conductive oxide layer is selected from the groupconsisting of titanium oxide, tin oxide and zinc oxide, respectively.

An advantage of this embodiment may be the relative ease with which suchPV may be produced. For instance, on known support material foils (seebelow), the metal oxide layer may be arranged, with techniques known inthe art (see also below).

Here, the flexible conductive composite foil may comprise a laminatecomprising a support material layer foil and the first electricallyconductive layer. Herein, a support material layer in the form of a foilis indicated as “support material layer foil”.

In general, the support material layer foil may be selected from thegroup consisting of iron foil, iron alloy foils, steel foils (includingfor instance foils of carbon steel, stainless steel, HSLA steel (highstrength low alloy), or tool steel), aluminium foil, copper alloy foils,brass (CuZn) foils, resistance foils (CuNi), nickel foils, silver foils,nickel silver foils, iron nickel foils (such as invar), and the firstelectrically conductive layer may comprise a layer selected from thegroup consisting of a titanium oxide layer, a tin oxide layer and a zincoxide layer, or of mixed oxides of two or more of these oxides.

In an embodiment, the support material layer foil comprises an iron foilor an iron alloy foil and the first electrically conductive layercomprises a titanium oxide layer. In another embodiment, the supportmaterial layer foil comprises an iron foil or an iron alloy foil, andthe first electrically conductive layer comprises a tin oxide layer. Inanother embodiment, the support material layer foil comprises an ironfoil or an iron alloy foil, and the first electrically conductive layercomprises a zinc oxide layer. Especially, the foil comprises an ironalloy foil, such as a steel foil. In another embodiment, the supportmaterial layer foil comprises an aluminium foil and the firstelectrically conductive layer comprises a titanium oxide layer. Inanother embodiment, the support material layer foil comprises analuminium foil and the first electrically conductive layer comprises azinc oxide layer. In yet another embodiment, the support material layerfoil comprises an aluminium foil and the first electrically conductivelayer comprises a tin oxide layer.

Such laminate comprising a support material layer foil and the firstelectrically conductive layer may for instance be obtained by providinga support material layer foil and providing by deposition thereon thefirst electrically conductive layer. Deposition may in an embodiment beelectrochemical deposition, may be spray pyrolysis or chemical vapourdeposition (optionally followed by calcination to provide the oxideskin). In another embodiment, deposition may comprise sputtering. Othertechniques known in the art may also be applied. An advantage of thelaminate comprising a support material layer foil and the firstelectrically conductive layer (wherein the first electrically conductivelayer is the conductive oxide layer) is that the first electricallyconductive layer may be very thin, such as in the range of about oneatomic layer (about 0.1 nm) up to about 100 nm, and that such embodimentmay be relatively easily produced. However, the layer thickness of thefirst electrically conductive (oxide) layer may also be up to about a 1μm. Especially, the first electrically conductive (oxide) layer may havea layer thickness in the range of about 20-100 nm. However, the layerthickness of the first electrically conductive (oxide) layer may also beup to about 2 μm.

The semiconductor material in a photovoltaic element according to theinvention is for instance zinc oxide, tin oxide or, preferably, titaniumdioxide. In an embodiment, combinations of two or more of these oxidescan also be applied as semiconductor material.

The layer of semiconductor material preferably comprises a layer ofphoto-sensitization material deposited thereon, in particular aphoto-sensitive dye, which is selected from suitable dyes known per sein the field.

The semiconductor material is a porous material, wherein within thepores, deposited on the semiconductor material photosensitizationmaterial is deposited. Thereon, an electrolytic liquid (or other holeconducting medium) is provided, also indicated as electrolyte.

Herein, the term “electrolyte” is used. This term is known to the personskilled in the art. Preferred electrolytes are based on iodine (i.e.iodide/iodine). Instead of an electrolyte, also other hole conductingmedia may be applied, such as for instance hole conducting polymers,such P3HT (poly(3-hexylthiophene)), or organic hole conductingmaterials, such as spiro-O-Me TAD. Therefore, in an embodiment, the term“electrolytic liquid” may be broader interpreted as “hole conductingmedium”, and thus the photosensitization material is in contact with ahole conducting medium, such as an electrolytic liquid, like aniodide/iodine based electrolyte, and the hole conducting medium is incontact with the catalyst layer.

The catalyst layer may comprise one or more catalysts selected from thegroup consisting of carbon, platinum and palladium, especially platinumand/or palladium, but may in an other embodiment also comprise acatalytically active conducting polymer, such as especiallypoly(dioctyl-bithiophene) (also known in the art as “PEDOT”).

The transparent substrate in a photovoltaic element according to theinvention especially comprises a foil of flexible plastic material (alsoindicated as transparent polymer foil), preferably polyethyleneterephthalate (PET) or polyethylene naphtalate (PEN), especially PEN,because of its relative advantageous thermal properties.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich FIGS. 1 a-1 c show in schematic cross-section non-limitingembodiments of a solar cell according to the invention. These figuresare not on scale.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 a and 1 b schematically show a stack or layered structure 25 ofa solar cell 1, which is substantially built up of a flexible conductivecomposite foil 23, a porous layer of nano crystalline titanium dioxide14 (or another semi conductor), a layer 15 of a suitable dye-sensitizer,a (lithium) iodide/iodine solution 16 (or another hole conducting mediumsuch as an iodide/iodine based electrolyte) and a transparent substrate26, especially a flexible foil 26, for instance PEN, on which a layer 18of a transparent conductive oxide (TCO) (such as indium tin oxide) isdeposited. Layer 15 is shown in greatly simplified manner. In realitythe dye sensitizer is applied in a solution to semiconductor layer 14and penetrates into the pores thereof, so that the dye covers the wholesemiconductor surface. The flexible conductive composite foil 23comprises a laminate of a support material layer foil 23 b and a firstelectrically conductive layer 23 a, which may in an embodiment also be afoil (FIG. 1 a).

The layer of titanium dioxide 14 may be formed in accordance with a perse known method by sintering a dispersion of colloidal particles oftitanium dioxide onto flexible conductive composite foil 23, whereinbetween the sintered titanium dioxide 14 and composite foil 23 a layerof oxide 28, such as titanium dioxide, is present, which protects theunderlying first electrically conductive layer 23 a against thecorrosive action of the hole conducting medium (such as lithiumiodide/iodine) 16.

The figure further shows a layer 19 (not shown to scale) of a catalyst,for instance carbon, for the conversion of neutral I in the lithiumiodide solution to iodine by accepting an electron fromcounter-electrode 18. In this solar cell 1 light (indicated by arrowsdesignated hv, wherein h represents Planck's constant and v thefrequency of the incident light) is incident on dye layer 15 viacounter-electrode or second electrically conductive layer 18 and thelithium iodide/iodine solution as hole conducting medium 16. Anothercatalyst may for instance be platinum or optionally palladium. In apreferred embodiment, Pt is applied as catalyst.

FIG. 1 a especially schematically shows an embodiment wherein the firstelectrically conductive layer essentially consists of first electricallyconductive layer 23 a, whereas FIG. 1 b schematically shows anembodiment wherein the first electrically conductive layer essentiallyconsists of first electrically conductive layer foil 123 a.

Hence, the invention provides solar cell or photovoltaic element 1,which is a layered structure or stack 25, comprising the flexibleconductive composite foil 23, including support material layer foil 23 band first electrically conductive layer 23 a, the oxide layer 28, thecrystalline metal-oxide semi-conductor layer 14, the photosensitizationmaterial 15, electrolytic liquid (or other hole conducting medium) 16,catalyst layer 19, transparent second electrically conductive layer 18and transparent flexible substrate 26.

The invention further provides a photovoltaic element 1 comprising alayered structure 25 of at least a first electrically conductive layer23 a, a layer of crystalline metal oxide semiconductor material 14deposited on the first electrically conductive layer 23 a, a layer ofphotosensitization material 15 deposited on the semiconductor material14 a transparent second electrically conductive layer 18 deposited on atransparent substrate 26, and a hole conducting medium (such as anelectrolytic liquid) 16 contained between the layer of semiconductormaterial 14 and the second electrically conductive layer 18, wherein thephotovoltaic element is flexible, the layer of semiconductor material 14is deposited on a flexible conductive composite foil 23, which flexibleconductive composite foil 23 comprises the first electrically conductivelayer 23 a and a support material layer foil 23 b, and the transparentsubstrate 26 is a foil of flexible plastic material.

In a specific embodiment, the first electrically conductive layer 23 acomprises a conductive oxide layer (see also above). Such embodiment isschematically depicted in FIG. 1 c, in contrast to the above describedembodiments, substantially no metallic tin, titanium or zinc is present(as layer), but substantially, only oxides of one or more of thosemetals are present. Hence, the conductive oxide layer 23 a and the(native) oxide layer 28 are in this embodiment one and the same layer,also indicated with reference 123 b, which refers to the firstelectrically conductive layer 23 a, wherein this layer is an oxidelayer, especially selected of one or more oxides of the group tin oxide,titanium oxide and zinc oxide. For instance, the support material layerfoil 23 b may be an iron or iron alloy foil, wherein with organo metalcompounds with Ti, Sn or Zn as metal, the respective oxides aredeposited by spray pyrolysis, thereby providing flexible conductivecomposite foil 23.

It is noted that the examples given here serve to elucidate theinvention, not to limit the scope thereof. A “reversed” dye-sensitizedsolar cell according to the invention can for instance also contain,instead of the above mentioned lithium iodide, another per se knownsuitable electrolytes such as potassium bromide/bromine or potassiumiodide/iodine, or other hole conducting mediums known in the art.

Referring to FIGS. 1 a-1 c, the crystalline metal-oxide semiconductorlayer is especially obtainable by sintering a dispersion of colloidalparticles of titanium dioxide onto flexible conductive composite foil23. In this way, nano porous metal oxide, like nano porous titaniumdioxide may be obtained, as known in the art.

The term “substantially” herein, such as in “substantially all emission”or in “substantially consists”, will be understood by the person skilledin the art. The term “substantially” may also include embodiments with“entirely”, “completely”, “all”, etc. Hence, in embodiments theadjective substantially may also be removed. Where applicable, the term“substantially” may also relate to 90% or higher, such as 95% or higher,especially 99% or higher, even more especially 99.5% or higher,including 100%. The term “comprise” includes also embodiments whereinthe term “comprises” means “consists of”.

Furthermore, the terms first, second, third and the like in thedescription and in the claims, are used for distinguishing betweensimilar elements and not necessarily for describing a sequential orchronological order. It is to be understood that the terms so used areinterchangeable under appropriate circumstances and that the embodimentsof the invention described herein are capable of operation in othersequences than described or illustrated herein.

The devices herein are amongst others described during operation. Aswill be clear to the person skilled in the art, the invention is notlimited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.Use of the verb “to comprise” and its conjugations does not exclude thepresence of elements or steps other than those stated in a claim. Thearticle “a” or “an” preceding an element does not exclude the presenceof a plurality of such elements.

The mere fact that certain measures are recited in mutually differentdependent claims does not indicate that a combination of these measurescannot be used to advantage.

1. A photovoltaic element (1), comprising a layered structure (25),wherein the layered structure (25) comprises: a. flexible conductivecomposite foil (23), including i. a support material layer foil (23 b)and ii. a first electrically conductive layer (23 a) comprising a layerselected from the group consisting of a titanium layer, a tin layer anda zinc layer; the first electrically conductive layer (23 a) in contactwith b. an oxide layer (28); the oxide layer (28) in contact with c. acrystalline metal-oxide semi-conductor layer (14); the crystallinemetal-oxide semi-conductor layer (14) in contact with d. aphotosensitization material (15); the photosensitization material (15)in contact with e. a hole conducting medium (16); the hole conductingmedium (16) in contact with f. a catalyst layer (19); the catalyst layer(19) in contact with g. a transparent second electrically conductivelayer (18); and the transparent second electrically conductive layer(18) in contact with h. a flexible transparent substrate (26).
 2. Thephotovoltaic element (1) according to claim 1, wherein the flexibleconductive composite foil (23) comprise a laminate comprising thesupport material layer foil (23 b) and the first electrically conductivelayer (23 a).
 3. The photovoltaic element (1) according to any one ofthe preceding claims, wherein the first electrically conductive layer(23 a) comprises a titanium layer.
 4. The photovoltaic element (1)according to any one of claims 2-3, wherein the first electricallyconductive layer (23 a) and the oxide layer (28) together have a layerthickness in the range of 20-100 nm.
 5. The photovoltaic element (1)according to claim 1, wherein the flexible conductive composite foil(23) comprises a laminate of a support material layer foil (23 b) and anelectrically conductive layer foil (123 a) as first electricallyconductive layer (23 a).
 6. The photovoltaic element (1) according toclaim 6, wherein the electrically conductive layer foil (123 a) is afoil selected from the group consisting of a titanium foil, a tin foiland a zinc foil.
 7. The photovoltaic element (1) according to any one ofclaims 6-7, wherein the electrically conductive layer foil (123 a) is atitanium foil.
 8. The photovoltaic element (1) according to any one ofthe preceding claims, wherein the support material layer foil (23 b) isselected from the group consisting of iron foil, iron alloy foil, steelfoil, aluminium foil, copper alloy foil, brass (CuZn) foil, resistancefoils (CuNi), nickel foils, silver foils, nickel silver foils, and ironnickel foils.
 9. The photovoltaic element (1) according to any one ofthe preceding claims, wherein the support material layer foil (23 b) isselected from the group consisting of iron foil and iron alloy foil. 10.The photovoltaic element (1) according to any one of the precedingclaims, wherein the transparent substrate (26) is polyethyleneterephthalate (PET) or polyethylene naphtalate (PEN).
 11. Thephotovoltaic element (1) according to any one of the preceding claims,wherein the transparent substrate (26) is polyethylene naphtalate (PEN).12. The photovoltaic element (1) according to any one of the precedingclaims, wherein the oxide layer (28) is the first electricallyconductive layer (23 a).
 13. A photovoltaic element (1), comprising alayered structure (25), wherein the layered structure (25) comprises: a.flexible conductive composite foil (23), including i. a support materiallayer foil (23 b) and ii. a first electrically conductive layer (23 a),wherein the first electrically conductive layer (23 a) is a conductiveoxide layer, wherein the first electrically conductive layer (23 a) is alayer obtained by providing a metallic layer and oxidizing said metalliclayer to provide the conductive oxide layer, wherein the metallic layeris selected from the group consisting of a titanium layer, a tin layerand a zinc layer; the first electrically conductive layer (23 a) incontact with b. a crystalline metal-oxide semi-conductor layer (14); thecrystalline metal-oxide semi-conductor layer (14) in contact with c. aphotosensitization material (15); the photosensitization material (15)in contact with d. a hole conducting medium (16); the hole conductingmedium (16) in contact with e. a catalyst layer (19); the catalyst layer(19) in contact with f. a transparent second electrically conductivelayer (18); and the transparent second electrically conductive layer(18) in contact with g. a flexible transparent substrate (26).